An ordinary No. 2 pencil contains graphite (from the Greek γράφω, graphō which means "to write" or "to draw").  Graphite conducts electricity and you can use your pencil and a piece of paper to draw your own potentiometer then experiment with it using the 555 test circuit.

Parts needed for pencil and paper potentiometer:

No. 2 pencil

Blank white 8 ½ X 11 sheet of printer paper

Clear adhesive tape such as Scotch tape (optional)

On the printer paper, draw a 1 cm X 20 cm rectangle and fill it in as completely and darkly as you can—the more graphite you use on the rectangular strip, the better it will conduct. My graphite strip runs all the way to the edge of the paper to make it easier to tape down one of the Snap Circuits jumper wires to the end of the strip (I needed a free hand to shoot the video).

Build the circuit shown

Parts Needed:

1 555 Timer IC (I used a KIA555p, but the NE555 will do just fine)

Snap Circuits Parts:

1 Base Grid (11” x 7.7”) # 6SC BG

1 Eight-Pin IC Socket # 6SC ?U8

0.02uF Capacitor # 6SC C1

1 Variable Resistor #6SC RV

1 Whistle Chip # 6SC WC

1 4.5 Volt Battery Holder # 6SC B3

1 Slide Switch # 6SC S1

Jumper Wire 18" (Black) # 6SC J1

Jumper Wire 18" (Red) # 6SC J2

1 Single Snap Conductor # 6SC 01

5 Conductor with 2-snaps # 6SC 02

2 Conductor with 3-snaps # 6SC 03

2 Conductor with 4-snaps # 6SC 04

1 Conductor with 5-snaps # 6SC 05

2 Conductor with 6-snaps # 6SC 05

As I demonstrate in the video, simply place the red jumper wire at one end of the strip so that the metal of the snap touches the graphite. Slide the black jumper wire (with metal of the snap touching the graphite) up and down the strip and listen to the changes in the tone on the speaker.


Similar instruments have been called Tannerins, or Electro-Theremins, but technically, since the 555 test circuit generates a square wave and a Tannerin generates a sine wave, you couldn't properly call it a Tannerin. Instead, you might call it a “555 Timerin.”

The change in pitch is caused by increasing or decreasing the resistance in the circuit. As you move the black snap farther away from the red snap on the graphite strip, the resistance in the circuit increases and the pitch of the tone gets lower. Conversely, as you move the black snap closer to the red snap, the resistance in the circuit decreases and the pitch of the tone increases.

The graphite strip is similar to a linear potentiometer, or “fader” like the Variable Resistor (RV) in the circuit. Here’s a video of the original circuit, that demonstrates the operation of the Variable Resistor (RV) and the change in pitch:

Let’s compare a potentiometer to a single pole single throw switch. The Slide Switch (S1) is like a light switch. When you switch it on it stays on. When you switch it off, it stays off. Using the water pipe analogy, you can think of a water tank with a pipe connected at the bottom. In the pipe is a valve with two states, open or closed. When the valve is closed no water can flow through the pipe:

Conversely, when the valve is open, water can flow through the pipe and drain out of the tank:

A potentiometer, on the other hand, is like a faucet. As you twist the faucet counter-clockwise (lefty loosey), it allows more and more water to flow through the pipe. As you twist the faucet clockwise (righty tighty) it allows less and less water to flow through the pipe:

In the following video I've replaced the Variable Resistor (RV), or linear potentiometer with the 500K potentiometer (RV3) from the Snap Circuits Sound set to continue the faucet analogy: